1. Field of the Invention
The present invention relates to structural analysis for an object that is formed by uniting a number of elements, and more particularly to generation of mesh data that is to be used for the structural analysis.
2. Description of the Related Art
Generally, finite element method has been widely applied to structural analysis, such as deformation analysis or residual vibration analysis, of an object formed by uniting a number of elements by means of screws and/or welding (for example, see Japanese Patent Application Laid-Open (KOKAI) No. HEI 6-331506).
Finite element method is an approximate analysis method for analyzing deformation and stress on an object using mesh data representing the object. Therefore in order to carry out structural analysis by finite element method, there has been provided a structural analysis apparatus incorporating a tool (software or the like) for generating mesh data by means of CAD (Computer Aided Design) on the basis of design data of an object that is to be analyzed.
A conventional mesh data generating apparatus however automatically generates mesh data for each of a number of elements that contribute to rigidity of the object but does not generate mesh data for connectors, e.g. screws (fastening screw) and/or welding materials, that make connections between the elements for the reason to be described later. Elements that are actually connected at connections by screws or welding materials are not connected in the generated mesh data. As a solution, an operator compares the generated mesh data with the corresponding design data generated by means of CAD or the like and manually makes, for future structural analysis, connections (engagement) between the elements in the mesh data using a mouse or another devices.
For example, a case for a notebook PC or a server has over 20 elements that contribute to rigidity. A notebook PC case is formed principally by uniting a lower cover, a frame, a print board, a DVD (Digital Versatile Disk) unit, an FDD (Floppy™ Disk Drive) unit, a HDD (Hard Disk Drive) unit and an upper cover by means of screws or welding.
Here, description will now be made in relation to a connection manner for elements that unitedly form a notebook PC case which connection is carried out manually by an operator with reference to FIGS. 17-21. First of all, the operator displays three-dimensional CAD design data shown in FIG. 17 representing the notebook PC case P on a monitor or the like and displays also mesh data shown in FIG. 18, generated based on the three-dimensional design data, by superimposing on the three-dimensional design data shown in FIG. 17 or in parallel with the three-dimensional design data so that connections (engagements) on the mesh data are found.
Then the operator enlarges a found connection (part S in FIG. 18) in the mesh data as shown in FIG. 19(a); finds nodes v and v′ corresponding to edges on each connection (engagement) between elements V and V′ respectively shown in FIGS. 19(b) and 19(c); and connects the nodes v and v′ of the elements V and V′ that are to be connected to each other in a manner of MPC (Multi Point Constraint) using the mouse to thereby connect the elements V and V′ to each other.
More specifically, if, for example, an upper element A and a lower element B shown in FIG. 20 each of which has a boss are connected to each other at a connection in the three-dimensional design data found in the above manner by a screw, nodes located on a connection at which one of the elements comes to closest to the other elements (here, a connection is the openings of the bosses of the elements (upper element A and lower element B) which bosses are facing to each other at the connection) which nodes are corresponding to edges at the connection in the mesh data as shown in FIG. 21 are selected and are MPC-connected. In this example, lines D make one-to-one connections between four nodes C on the upper element A and four nodes C on the lower element B.
FIGS. 20 and 21 extract only a connection from the enlarged mesh data as shown in FIG. 19(a) for visual convenience of the found connection. Actually, nodes corresponding to edges on the connection are found from the enlarged mesh data shown in FIG. 19(a) and the found nodes are connected to each other.
Further, in the same manner as the connecting manner performed on the notebook PC case P described with reference to FIGS. 17 to 21, mesh data concerning a server case Q is connected by enlarging the connection (here a part T in FIG. 22) on the monitor as shown in FIG. 23(a); finding nodes w and w′ corresponding to edges of the connection on elements W and W′ respectively as shown in FIGS. 23(b) and 23(c); and carrying out MPC connection on the nodes w and w′ so that the elements W and W′ are connected to each other.
A notebook PC case has approximately 100 connections by means of screws or welding, and a server case has as many as approximately 300 connections.
Manually connecting two elements at each of such a large number of connections forces an operator into a great deal of load and time.
In order to find nodes corresponding to edges at each connection in design data from mesh data, the operator has to enlarge the connection in the mesh data being displayed on the monitor, comparing to the design data. That results in defective workability and defective operating efficiency loaded on the operator.
As a solution, design data concerning connectors such as screws (fastening screws) or welding materials may be converted in mesh data, in other words, mesh data in which connections between elements are connected is automatically generated. For example, design data concerning a single screw is converted into mesh data, which has 2,000-4,000 meshes (mesh elements), so that conversion of screws into mesh data adds far more than 200,000 meshes to the mesh data concerning a notebook PC case or a server case because the cases have 100 or more connections.
As conducting structural analysis by finite element method, the ordinary upper limit of the number of meshes in mesh data corresponding to an object is considered to be 150,000 to 200,000 meshes due to performance of a computer that carries out structural analysis. It takes extremely long time to accomplish structural analysis applied to mesh data including an excessive number of meshes.
Therefore, a conventional technique does not practically generate mesh data in which elements are connected also by converting connectors exemplified by screws and/or welding materials into mesh data.